Crude oils, residual oils, and middle distillates contain various amounts of n-paraffin, depending on their origin and method of production. Low temperatures reduce the solubility of these paraffins, which separate out as platelet-shaped crystals which can agglomerate and grow into one another in honeycomb fashion, sometimes including oil. The flow properties of the crude oils and crude oil products are thereby considerably impaired, so that problems may arise in their delivery, transportation, storage, and use.
The pour point (abbreviated PP; determined in accordance with DIN 51597) is an important applicational parameter for characterizing the flow and low temperature properties of crude and residual oils. The flow and low temperature properties of middle distillates are described by the cold filter plugging point (abbreviated CFPP; determined in accordance with DIN 51428). Both parameters are measured in .degree.C.
It is known to add additives to mineral oils which modify the size and shape of the paraffin crystals and improve the low temperature properties of such oils, so that they remain flowable and filterable even at low temperatures. Pour point depressants are added to crude and residual oils to reduce the PP and flow improvers are added to middle distillates to reduce the CFPP. Oil-soluble copolymers of ethylene with other monomers have acquired great importance as pour point depressants and flow improvers.
Thus, according to DE-B-11 47 799, oil-soluble copolymers of ethylene and vinyl acetate having molecular weights between about 1,000 and 3,000 are added to petroleum distillates, engine fuels, or combustion fuel mixtures having a boiling range between about 120.degree. and 400.degree. C. Copolymers which comprise about 60% to 99% by weight of ethylene and about 1% to 40% by weight of vinyl acetate have proven to be particularly suitable.
The use of terpolymers containing at least 60% by weight of ethylene units, 1% to 40% by weight of alkenecarboxylic acid ester and/or vinyl ester units, and 1% to 30% by weight of vinyl ketone units having a molecular weight of 500 to 20,000, as additives for crude oils and middle distillates, is known from DE-A-32 47 753.
Terpolymers of ethylene having an average molecular weight of 500 to 10,000 are described as additives for crude and residual oils in U.S. Pat. No. 4,015 063. In addition to 45% to 80% by weight of ethylene, they comprise 10% to 30% by weight of a dialkylvinylcarbinol and 10% to 25% by weight of a fatty acid vinyl ester having up to 8 carbon atoms.
The use of terpolymers having an average molecular weight of 500 to 10,000 and comprising, in addition to ethylene, 0.5% to 20% by weight of diisobutylene and 20% to 35% by weight of vinyl acetate, as additives for mineral oils and mineral oil distillates, is known from EP-B-2 03 554.
EP-A-3 09 897 describes copolymers of 95% to 50% by weight of ethylene and 5% to 50% by weight of vinyl methoxyacetate having an average molecular weight of 500 to 10,000 and their use as flow improvers for middle distillates.
DE-A-40 42 206 relates to terpolymers which comprise, in addition to ethylene, 5% to 35% by weight of vinyl acetate and 1% to 25% by weight of vinyl neononanoate or vinyl neodecanoate and have an average molecular weight of 500 to 5,000. They are used as flow improvers, in particular for middle distillates.
Polymeric flow improvers for middle distillates, based on graft polymers which comprise 20% to 80% by weight of methacrylic acid esters of C.sub.8 - to C.sub.15 -alkanols and 80% to 20% by weight of ethylene/vinyl acetate copolymers having a degree of branching of 3 to 15 CH.sub.3 groups per 100 CH.sub.2 groups, are known from DE-A-37 25 059.
A disadvantage of the known pour point depressants and flow improvers is that their activity is not adequate for mineral oils and mineral oil distillates of particular origins and/or methods of production; for example, in middle distillates having final boiling points above 380.degree. C., the cloud point is quite often significantly above 0.degree. C. Furthermore, the use of conventional flow improvers can lead to impairment of the filterability of mineral oil distillates above the cloud point.